A multitude of techniques for shaping (such as stamping, grinding, and milling) and joining (such as welding and mechanical joining) metals are highly developed for the fabrication of macroscopic structures. Application of these techniques to the fabrication and assembly of metallic microstructures (structures having features <100 μm) becomes increasingly difficult as the feature sizes become smaller. For that reason, new approaches to microfabrication that are not derived from fabrication techniques used on a large scale have been developed. A widely used technique for fabrication of metallic microstructures is microelectrodeposition of metals on an appropriately shaped mandrel or template. Two examples of this class of processes are through-mask electroplating and LIGA (Lithographie, Galvanoformung, Abformung), both of which are based on projection photolithography (for LIGA, commonly carried out using x-rays, although the availability of the SU-8 class of photoresist has reduced the need for x-ray exposure in making thick structures). Although these methods provide ways to form metallic microstructures, they are processes with several steps, and require facilities of limited availability.
Recently, methods for the microfabrication of metallic, 2D and 3D structures based on the combination of soft lithography and microelectrodeposition have been described, the latter both through a mask of photoresist and onto patterned, conducting surfaces. The pattern-transfer step in these soft lithographic techniques typically uses an elastomeric stamp with a surface relief structure that carries the desired pattern. These stamps are usually formed by molding polydimethylsiloxane (PDMS) against a ‘master’ composed of a relief pattern in photoresist, and obtained by photolithography. These masters may be generated using a technique based on high-resolution commercial printing and high-resolution optical reduction. This procedure is efficient from design, through stamp, to initial structure typically requires no more than 24 hours. Both the preparation of the mask and the generation of the master by photolithography may require access to specialized devices and facilities (i.e., high-resolution image setters, clean rooms) that are more readily available than the mask-making facilities required in high-resolution photolithography, but that are still not available to every laboratory that might benefit from medium resolution microfabrication.